Controlling apparatus for refrigerating systems



March 30,1937. F, H, HIBBE D 2,075,647

CONTROLLING APPARATUS FOR REFRIGERATING SYSTEMS Filed Nov. 28, 1954INVEN TOR. E'edevick Iifibberol I H15 ATTORNEY UNITED STATES PATENTOFFICE:

CONTROLLING APPARATUS FOR REFRIG- ERATING SYSTEMS Frederick H. Hibberd,Larclimont, N. Y. assignor to Ingersoll-Rand' Company, Jersey City, N.it, a corporation of New Jersey Application November 28, 1934, SerialNo. 755,140

13 Claims.

This invention is an improvement in controlling apparatus, especiallyfor a refrigerating system, to facilitate operation at reduced output.

The invention is adapted for use with a refrigerating system in which anon-volatile refrigerant, such as water, is cooled by vaporizing partthereof, and in which a compressor of the centrifugal type running atconstant speed carries off the vapor thus formed. Such a systemcomprises an evaporator vessel to which the liq- 5 varies widely inpractice, the system must be capable. of working without loss ofstability at all refrigerating loads.

It is well known that a centrifugal compressor performs well over aconsiderable part of its load range, but that when the load thereon isconsiderably diminished, the vapor in the compressor has acharacteristic-tendency to break back or surge. Surging of the vaporrenders the load on the compressor unstable; that is, the volumedelivered and the intake and discharge pressures of the compressorfluctuate considerably. Such surging occurs when the compression-ratioof the compressor exceeds a critical value, and when the volume of fluiddelivered to the compressor is insufficient to satisfy its volumetriccapacity.

When coupled in a refrigerating system of the kind above-mentioned, theliability of surging of the vapor in the compressor is counteracted to agreat degree by changes in the density and volume of the water vaporentering the compressor. But the tendency remains and instability ofload will appear when the load is very light.

The chief object of this invention is to obviate entirely the liabilityof surging of the vapor in the compressor or blower at low loads securedin connection with the removal of water vapor and the transmissionthereof to a suitable condenser, thereby assuring smoothness ofoperation and elimination of all danger of damage tothe blower and motorfor same.

Another object of the invention is to maintain stable load on thecompressor by introducing vapor from the condenser into the inlet sideof the compressor and automatically controlling the introduction of saidvapor by means acting in accordance with the compression-ratio developedby the compressor.

In-the operation of a centrifugal compressor in a water vaporrefrigerating system, the degree of compression increases as the loaddecreases, that is, the ratio of the discharge pressure to the suctionpressure varies inversely as the load thereon and hence, inversely asthe load on the system. My invention takes advantage of this conditionto keep the by-pass closed over a large range of load, and includes anauxiliary positive displacement compressor which produces a pressurethat is higher than that of the centrifugal compressor except at suchlow loads as will permit surging of the vapor to commence. At such atime the pressure produced by the centrifugal compressor becomes greatenough to exceed the pressure produced by the auxiliary device, and atonce'actuates suitable connections that open the by-pass. Some of thevapor discharged by the compressor is then returned to the intake andall tendency to surge is nullified.

The nature and advantages of the invention are set forth in the drawingand accompanying description which disclose a preferred embodiment ofthe invention. But while I illustrate in outline a refrigerating systemhaving controlling means according to the invention, the -apparatusshown is of course only one embodiment of the a principle and variousalterations may be made, though not shown herein, such as changes in theform and arrangement of the various parts, within the scope or spirit ofthe appended claims. I

On the drawing the figure shows in outline an apparatus in whichthe'invention is incorporated.

The numeral l indicates an evaporator to which a liquid refrigerant,such as water, is admitted in a state of division by way of a spraynozzle 2 connected to an inlet or supply pipe 3. The pressure in theevaporator l is low enough to cause some of the water at the inlettemperature thereof to be converted into vapor as it enters. Thevaporization extracts heat from the remainder of the water and thus,cools oil the main body of the liquid. The chilled water is thendelivered from the evaporator and conveyed by means of a conduit 4 to aplace where a refrigerating effect is desired. As the water is vaporizedthe vapor is extracted from the evaporator by means of a centrifugalcompressor or blower 5. The intake of this blower communicates with theevaporator through a suitable port or passage, .and after compression inthe blower the vapor is delivered to a condenser 6 where it isliquefied. Both thev intake and the outlet of the blower are preferablypermanently open and of substantially fixed cross sectional area, theblower or compressor being of any suitable construction and comprisingone or more stages.

The compressor ti can be rotated by a steam turbine or electric motorwith step-up gearing between the driving unit and the compressor so thatthe compressor will always be revolved at constant high speed regardlessof whether the load increases or decreases. The compressor simply floatsas it were, on the load as the load varies from full load to part load,and the com-= pressor is to that extent self-regulating. Whenever a dropin load takes place the final temperature of the chilled water alsodrops and the compressor consumes less power although the speed does notchange. When the load diminishes, the pressure of the water vapor in theevaporator falls and there are an accompanying decrease in the densityof the water vapor and an increase in the specific volume thereof. Atgreater load the water vapor is compressed at greater density and lowerspecific volume, while at low load it is compressed at greater specificvolume-and less density. At full load or over, the ratio of compressionbetween the discharge pressure of the compressor and the inlet orsuction pressure, which is the pressure of the vapor in the evaporator,is relatively small, but this ratio of compression increases steadily asthe load falls off. Due to the fact that as the-load decreases thepressure within the evaporator decreases and the density and weight ofthe water vapor formed similarly decrease, the actual volume of vapordelivered to the compressor remains substantially constant in much thesame way as it would it an ordinary damper were placed at the inlet of'acompressor of this type. The machine thus operates to a large extent asa constant volume blower. The surging point is not apt to be reached atordinary part loads, but may be a rived at if the load becomes verylight.

In the event then that surging of the vapor occurs, as when therefrigerating system is delivering only a small part of its ratedoutput, the

load on the compressor becomes unstable and the volume delivered and theinlet and discharge pressures fluctuate considerably. The running of thecompressor becomes uneven and some fluctuations in the power supplied todrive the motor also arise. To obviate this at light loads I connect tothe condenser G and to the evaporator l a by-pass pipe I. This pipe willreturn part of the water vapor to the evaporator at light load and thusincrease the pressure and volume of the water vapor passing into thecompressor so that any tendency to surge is eliminated. The bypass pipe1 contains a valve 8 which is normally closed, but is automaticallyopened when the surging point is approached. To control this valve Itake advantage of the fact that the ratio of compression of thecompressor 5 rises as .theload or output decreases and at low load asthe surge point is approached it becomes high enough to enable thedischarge pressure of the blower 5 to be applied to open the valve 8 andenable some of the vaporsin the condenser 6 to return to the evaporatorI.

To utilize the discharge pressure of the compressor 5 in this way andmake it otherwiseineffective, I provide a container 9 and connect thecontainer at the bottom through a trap forming pipe ID with the bottomof the condenser 6. In the container 9 is a float ll carried by abellcrank lever mounted on a pivot l2. This lever is joined by a rod orlink l3 to one end of an outbut such action is not detrimental. loaddecreases however, the pump I! being a aovaecr a link connected to anoutside arm on the rotary valve 53. As the vapor delivered by blower 5is condensed it collects at the bottom of the condenser t and flowsthrough the pipe it and into the container 9. The top of the container dis connected by a pipe E9 to the discharge port of a small positivedisplacement compressor or pump ill, either of the rotary orreciprocating type. The intake port of this compressor ill is connectedby a pipe it to the evaporator. The compressor ll, preferably runing ata constant speed, withdraws a small portion of vapor from the evaporatorand discharges it into the container 9. Most of the condensing of thisvapor will occur in the container 9, and the pressure in the containerwill depend on a number of factors: the speed of the pump ill, thecapacity of pump ill and pipes i6 and it, the volume of the chamber 9(which acts as an expansion chamber) and the rate of condensation in thechamber ll which is dependent upon the surface area of the liquidtherein. By proper design and control of these factors I am enabled tocontrol the pressure in the container at will. Suffice it to say at thepresent that the pressure produced in the container 9 will beconsiderably higher than the condenser pressure at all normal loads but,as the load approaches the critical minimum at which surging will occur,the container pressure will decrease much more rapidly than does thecondenser pressure and the liquid level in the container will rise. Thefloat M will normally be held in such a position that it will be out ofthe water in the container 9 and thereby hold the valve 3 in closedposition. However, as the load falls, the rising liquid level in thecontainer will at the desired moment engage the float H and cause thevalve 8 to open. The pressure in the evaporator will then increase orat' least be prevented from falling below the critical minimum, and anequilibrium will be established between evaporator, condenser andcontainer pressures, and'the position of the valve 8 will be determinedaccordingly. Thus the purpose of the pump ill is to produce a pressurewhich will be dependent among other things upon the pressure in theevaporator but which will exceed the condenser pressure at normal loadsand which will be approximately the same as condenser livered by thepump 11, although considerably less than that of the blower 5, will besufficiently great to build up a pressure in the container 9considerably in excess of the pressure in the condenser 6. The water inthe container is then. depressed until equilibrium between the condenserand container pressures is attained. Vapor at such normal loads may evenblow through the pipe l0 and into the condenser 6 When the constantvolume pump delivers ever decreasing weights of vapor, and suchdecreased weight of vapor is more easily and more quickly condensed inthe container 9. The pressure therein inevitably decreases because ofthis fact and because of the fact that the actual compression producedin the pump I1 is much less than before. The liquid rises in thecontainer and, with proper design, engages the float H to cause thevalve 8 to open just shortly before the low load occurs tain thepressure in the evaporator above a cerat which the load on the blowerbecomes unstable.

The small motor driven compressor I1 is built for a compression ratiogiving a compression 5 slightly less than the peak of compressionreached The bottom of the condenser can be connected to the upper partof the evaporator l through 20 a U-shaped pipe I8, so that the liquefiedwater vapor can be returned to the evaporator I. This pipe acts as atrap because some water will always be in the bend thereof andcommunication cannot be directly established between the condenser 25and the evaporator I. The small volume of vapor withdrawn from theevaporator l by the pump iii in general condenses in the container 9,but as the wateris drawn out of the condenser through the pipe it asfast as it reaches the height of the 30 entrance to this pipe, the levelof the condensate in the condenser remains virtually constant and hencethere is no risk of the water rising too high in the condenser 6. Sincethe condensate level in the container 9 corresponds to the dif- 35ference in pressure between the container d and the condenser t, itcannot rise greatly above the condensate level in the condenser and thusthere is no danger of flooding the container.

This construction has the effect of so greatly 40 extending the range ofload stability for the compressor 6 that the risk of instability oi loadat even light loads is entirely nullified. Surging of the vapor is thusprevented entirely and the system can be operated at any point in itsrange from the lightest load to overload with perfect safety to thecompressor and its motor and all of the driving parts connected to same.4

I claim: 1. The combination with an evaporator having a plurality ofevacuators therefor, one or more of said evacuators developing a ratioof compression variable with the load on the evacuators, of means actingin accordance with the discharge pressures of said evacuators tostabilize the load on the evacuators as said ratio of compressionapproaches a critical value.

2. The combination with an evaporator having a plurality of evacuatorsfor removing vapor therefrom, of means subjected to the dischargepressures of all said evacuators and acting at low evacuator loads tostabilize the,pressure in the evaporator.

. 3. The combination with an evaporator having a plurality of evacuatorsfor removing vapor therefrom, of means subjected to the dischargepressures of said evacuators and acting in accordance with saidpressures and as the load on the evacuators drops to maintain thepressure in the evaporator above a certaincritical minimum. 4. Thecombination of an evaporator and evacuator means for the evaporator, acompressor for withdrawing a portion of vapor from the evaporator, andmeans acting in accordance with the difference in the dischargepressures of said 75 evacuator means and said compressor to aimtaincritical minimum and thereby stabilize the load on the evacuator means.

5. The combination of an evaporator and means for evacuating theevaporator, a 'condenser to receive the discharge of said means, acompressor for withdrawing a portion of vapor from the evaporator, andmeans subjected to the pressure in the condenser and the dischargepressure of said compressor and acting in accordance with said pressuresto control the pressure 1 in the evaporator.

6. The combination of an evaporator and means for evacuating theevaporator, a by-pass around said evacuating means, a compressor forwithdrawing a portion of vapor from the evaporator, and means acting inaccordance with the discharge pressures of said evacuating means andsaid compressor to control said by-pass.

7'. The combination of an evaporator and means for evacuating theevaporator, a by-pass around said evacuating means, a condenser to whichthe evacuating means discharges, a compressor for withdrawing a portionof vapor from the evaporator, and means acting in accordance with,

the pressure in the condenser and the discharge pressure of saidcompressor to open said by-pass as the load on said evacuating meansdrops.

8. The combination of an evaporator and evacuating means therefor, aby-pass around the evacuating means, a condenser to receive thedischarge of the evacuating means, a compressor for withdrawing aportion of the vapor from the evaporator, and means acting in accordancewith the difference between the discharge pressure of the compressor andthe pressure in the condenser to control said by-pass and therebycontrol the pressure in the evaporator. v

9. The combination of an evaporator and a compressor for removing vaportherefrom, said compressor having a compression ratio which variesinversely as the load thereon, a condenser to which the compressordischarges, a by-pass around the compressor, a positive displacementpump for withdrawing a portion of vapor from the evaporator, a containerto which the pump delivers, a conduit between the condenser and thecontainer, and means in the container acting in accordance with thedifference in the pressure in the condenser and the discharge pressureof the pump to control .said by-pass.

10. The combination of an evaporator and a centrifugal compressor forremoving vapor there from, means connected to be actuated by a forcecorresponding to the compressor discharge pressure to maintain thepressure in the evaporator above a certain critical minimum and therebymaintain stable load on the compressor, and means for rendering saidforce ineffective 'except when said pressure approaches said minimum.

11. The combination of an evaporator and a centrifugal compressorforremoving vapor therefrom, a by-pass around the compressor, meansconnected to be actuated by a force corresponding to the compressordischarge pressure to control said by-pass and thereby control thepressure in the evaporator, and means for rendering said forceineffective except when the pressure in the evaporator approaches acertain critical minimum.

12. The combination of an evaporator and a compressor for removing vaportherefrom, said compressor having a compression-ratio which variesinversely as the load thereon, a positive displacement pump for removinga portion of the vapor from the evaporator, the pump discharge pressurebeing normally greater than the com-= pressor discharge pressure, andmeans subjected to said discharge pressures and acting to efiect anincrease in the pressure in the evaporator when said compressordischarge pressure becomes greater than said pump discharge pressurethereby maintaining said evaporator pressure above 10 a certain criticalminimum.

answer 13. The method of stabilizing the load on a centrifugalcompressor which consists in opposing a force corresponding to thecompressor discharge pressure with a normally greater force. reducingthe said forces disproportionately as the load drops, and effecting anincrease of the compressor intake pressure when the difference in saidopposed forces approaches a certain critical value.

